Sensation and Perception Chapter 4

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Sensation and PerceptionChapter 4

• AP Psychology
• Forest Grove High School
• Mr. Tusow

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The Basics

• We do not actually experience the world directly,
  but instead we experience it through a series of
  filters we call senses.
• The study of these sense and their effect on our
  behavior is called sensory psychology.

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Sensation

• Sensation The process by which a stimulated
  receptor (eyes, ears) creates a pattern of
  neural messages that represent the stimulus in
  the brain, giving rise to our initial experience
  of the stimulus.

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Our Senses

• You will notice that all of our sense organs are
  very much alike.
• They all transform physical stimulation (such as
  light waves or sound waves) into the neural
  impulses what give us sensations (such as light
  and dark).

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Perception

• Perception A mental process that elaborates and
  assigns meaning to the incoming sensory patterns.
• Perception creates an interpretation of sensation.

Do you see faces or vases?
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Sensation and Perception

• Perception is essentially an interpretation and
  elaboration of sensation. Therefore, sensation
  refers to the initial steps in the processing of
  a stimulus.

These pictures look fairly similar
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The True Picture
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The Famous Mona LisaFrown or Smile
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The Famous Mona LisaFrown or Smile
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Big Idea

• Although it seems the brain interacts directly
  with the outside world, it does not.
• The brain senses the world indirectly because the
  sense organs convert stimulation into the
  language of the nervous system neural messages.
• In short, the brain never receives stimulation
  directly from the outside world.

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Transduction Changing Stimulus to Sensation

• In all the sense organs, it is the job of sensory
  receptors to convert incoming stimuli information
  into electrochemical signalsneural activity.
• Transduction The sensory process that converts
  energy, such as light or sound waves, into the
  form of neural messages.

Transduction with Hearing
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• The neural impulse carries a code of the sensory
  event in a form that can be further processed by
  the brain.

Light Waves
Neural Signals
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The Process of Transduction

• Transduction begins with the detection by a
  sensory neuron of a physical stimulus.
• When the appropriate stimulus reaches the sense
  organ, it activates specialized neurons called
  receptors.
• The receptors respond by converting their
  excitation into a nerve signal.
• Think of this as the way a bar-code reader
  converts a series of lines into an electrical
  signal that a computer can match with a price.

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A Simple Example

• Close both of your eyes. Press gently in the
  corner of one eye. You should see a pattern
  caused by pressure of your finger, not by light.
• These light sensations are phosphenes, or visual
  images caused by fooling your visual system into
  thinking it sees light.

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Sensory Adaptation

• Sensation is critically influenced by change.
  Thus, our sense organs are change detectors.
• Their receptors specialize in gathering
  information about new and changing events.

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Sensory Adaptation

• Sensory adaptation is the diminishing
  responsiveness of our sensory systems to
  prolonged stimulation.
• Unless it is quite intense or painful,
  stimulation that persists without change in
  intensity usually shifts to the background of our
  awareness.
• Until now, many of you are probably unaware that
  your sense of touch had adapted to the pressure
  of the chair against your legs.

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Thresholds

• What is the weakest stimulus that an organ can
  detect?
• Absolute threshold The level of stimulus
  necessary for a stimulus to be detected.
• Operational definition of absolute threshold The
  presence or absence of a stimulus is detected
  correctly half the time over many trials.

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• Because there is a fuzzy line between detection
  and nondetection, a persons absolute threshold
  is not necessarily absolute.
• It varies continually with our mental alertness
  and physical condition

Detection of Threshold
Sense Modality
Light A candle flame at 30 miles on a dark, clear night.
Sound The tick of a mechanical watch under quiet conditions at 20 feet.
Taste One teaspoon of sugar in two gallons of water.
Smell One drop of perfume diffused into the entire volume of a three-bedroom apartment.
Touch The wing of a bee falling on your cheek from a distance of one centimeter.
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Thresholds

• Difference thresholds The smallest amount by
  which a stimulus can be changed and the
  difference be detected, half of the time.
• Think about when you are watching TV and a
  commercial comes on. Can you tell a difference?

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Just Noticeable Difference

• Just Noticeable Difference (JND) The minimal
  amount of change in the signal that is still
  recognizable.
• Just noticeable difference, JND and difference
  threshold are used interchangeably.

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Laws of Sensation

• Webers Law The size of JND is proportional to
  the intensity of the stimulus the JND is large
  when the intensity of the stimulus is high.
• Fechners Law Expresses the relationship between
  the actual magnitude of the stimulus and its
  perceived magnitude.
• Stevens Power Law A law of magnitude that is
  more accurate than Fechners law and covers a
  wider variety of stimuli.

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Signal Detection Theory

• Signal detection theory says that sensation
  depends on the characteristics of the stimulus,
  the background stimulation and the detector.
• This theory takes the observers characteristics
  into account and says that stimulus judgment
  often happens outside of consciousness.

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Signal Detection Theory

• Signal detection theory recognizes that the
  observer, whose physical and mental
  characteristics are always in flux, must compare
  a sensory experience with ever-changing
  expectations and biological conditions.

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Subliminal Persuasion

• Advertising executive James Vicary announced that
  he had discovered an irresistible sales technique
  called subliminal advertisement.
• He said he could present images so quickly that
  the conscious mind would not perceive them, but
  the unconscious mind would, and the images would
  work on the viewers desires unnoticed.
• As to be expected, the public was outraged, but
  fascinated. People began worrying that they were
  being manipulated by powerful psychological
  forces.
• Lets try it now!!!!

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A_ _OM_BI_E
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Do Subliminal Messages Work?

• Based on studies, some people do respond to
  stimuli below the absolute threshold, under some
  circumstances.
• The problem is people behave different thresholds
  at different levels, so what could be subliminal
  (or below the threshold) for one person, may be
  supraliminal (above the threshold) for another
  person.

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Simplest Explanation

• The simplest explanation for reports of success
  with subliminal persuasion lies in the
  purchaser's expectations and in the need to prove
  they did not spend their money foolishly.

The same reason we read horoscopes!
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Backmasking- More Subliminal Messaging? Listing
to Songs in Reverse

• There are legend about hidden messages in songs.
  Led Zeppelin's Stairway to Heaven was one of the
  first songs to have supposed hidden, satanic
  messages.
• http//jeffmilner.com/backmasking.htm
• Why does this seem to work?

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How our Senses are Alike

• Vision, hearing, smell, taste, touch, pain and
  body position are all similar for three reasons.
• First, they all transduce stimulus energy into
  neural impulses.
• Second, they are all more sensitive to change
  than to constant stimulation.
• Third, they all provide us with information about
  the environment we are in.

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How Our Senses are Different

• With the exception of pain, all the senses taps a
  different form of stimulus, and each sends the
  information it gathers to a different part of the
  brain.
• The senses all operate in much the same way, but
  each extracts different information and sends it
  to its own specialized processing region of the
  brain.

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See a bell or hear a bell?

• Different sensations occur because different
  areas of the brain become activated. Whether you
  hear a bell or see a bell depends ultimately on
  which part of the brain receives stimulation.

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Vision

• Vision is the most complex, best developed and
  most important sense for humans and other highly
  mobile creatures.
• Think of the eye as the brains camera.
• It gathers light, focuses it, converts it to a
  neural signal and sends these signals on for
  further processing.

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How the Eye Works

• The eye transduces the characteristics of light
  into neural signals that the brain can process.
• This transduction happens in the retina, the
  light sensitive layer of cells at the back of the
  eye.

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How the Eye Works
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Photoreceptors

• Photoreceptors Light-sensitive cells (neurons)
  in the retina that convert light energy into
  neural energy.
• Rods Photoreceptors that are especially
  sensitive to dim light, but not color.
• Cones Photoreceptors that are especially
  sensitive to colors but not dim light.
• Cones are responsible for our ability to see
  colors.

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Photoreceptors Rods, Cones
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The Fovea

• The fovea is the area of sharpest vision.
• It has the highest concentration of rods and
  cones.

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The Optic Nerve and The Blind Spot

• Optic Nerve The bundle of neurons that carries
  the visual information from the retina to the
  brain.
• This is where the stimulus, once changed into a
  neural impulse, gets passed onto the brain.
• Blind Spot The point where the optic nerve exits
  the eye and where there are no photoreceptors.
  Any stimulus that falls on this area cannot be
  seen.

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Example From the Book

• In your book, turn to page 122. Read the section
  titled DO IT YOURSELF!
• Try both the demonstrations.
• Can you make the disappear?
• Can you make the line solid?
• This phenomenon is a result of our blind spots.

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The Visual Cortex

• In the visual cortex, the brain begins working by
  transforming neural impulses into visual
  sensations of color, form, boundary and movement.
• This process is called parallel
  processing-simultaneous processing of several
  aspects of a problem simultaneously

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• Different parts of the visual cortex are used to
  identify different images

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Why we Dont Have Sensory Adaptation In Vision
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After Images

• Stare at the eye of the red parrot while you
  slowly count to 20, then immediately look at one
  spot in the empty birdcage. The faint, ghostly
  image of a blue-green bird should appear in the
  cage.

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Explanation of Ghostly After Images

• The ghostly birds are called afterimages.
• As you stare at the red bird, light-sensitive
  cells at the back of your eyes become less
  responsive to red light. This is called the
  opponent processing theory.
• Opponent Processing Theory there are some color
  combinations that we never see, such as
  reddish-green or yellowish-blue.
• Color perception is controlled by the activity of
  two opponent systems a blue-yellow mechanism and
  a red-green mechanism
• When you shift your gaze to the birdcage, your
  visual system subtracts red light from the
  white light thats being reflected from the white
  background. White light minus red light is
  blue-green light.

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Continued Processing

• With further processing, the cortex combines
  these sensations with memories, motives,
  emotions, and sensations to create a visual world.

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A Colorless World

• Despite the way the world appears, color does not
  exist outside the brain, because color is a
  sensation that the brain creates based on the
  wavelength of light striking our eyes.
• Color is created when the wavelength in a beam of
  light is recorded by the photoreceptors in the
  form of neural impulses.
• It is then sent to specific regions of the brain
  for processing.

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Color Blindness

• Not everyone sees color in the same way, because
  some people are born with a color deficiency.
• While some people can see no color at all, and
  are totally color blind, it is rare.
• More common is color weakness, where people have
  a hard time distinguishing between certain colors.

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The Spectrum of Electromagnetic Energy
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Vision- Physical Properties of Waves
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The Visual Pathway
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Hearing

• The vibrational energy of vibrating objects, such
  as guitar strings, transfer the surrounding
  medium-air-as the vibrating objects push the
  molecules of the medium back and forth.
• In space, there is no air, so the sound wave
  would have no medium to push. Any explosion would
  be eerily without sound.

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Frequency and Amplitude

• There are two physical characteristics of sound
  frequency and amplitude.
• Frequency The number of cycles completed by a
  wave in a given amount of time-determines pitch.
• Amplitude The physical strength of a wave-the
  volume of the sound.

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The Process of Hearing

• The middle ear transmits the eardrums vibrations
  through a piston made of 3 small bones (the
  hammer, anvil and stirrup) to the cochlea (snail
  shaped tube).
• The incoming vibrations cause the cochleas
  membrane (oval window) to vibrate, moving the
  fluid that fills the tube. This motion causes
  ripples in the basilar membrane (hair cells).
• The movement of cells triggers impulses in the
  adjacent nerve fibers which from the auditory
  nerve that connects via the thalamus to the
  temporal lobe.

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see pages 126-127 for more info
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Audition

• Place Theory
• the theory that links the pitch we hear with the
  place where the cochleas membrane is stimulated
• Frequency Theory
• the theory that the rate of nerve impulses
  traveling up the auditory nerve matches the
  frequency of a tone, thus enabling us to sense
  its pitch

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How We Locate Sounds
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If a tree falls in the forest

• The question If a tree falls in the forest and
  there is no one around to hear it, does it still
  make a sound? can now be answered.
• No, it would make no noise.
• Sound is a purely psychological sensation that
  requires an ear (and the rest of the auditory
  system) to produce it.

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Deafness

• There are generally two types of deafness.
• Conduction deafness is an inability to hear,
  resulting from damage to the structures of the
  middle or inner ear.
• Nerve deafness (Sensorineural Deafness) is an
  inability to hear, linked to a deficit in the
  bodys ability to transmit impulses from the
  cochlea to the brain.

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Position and Movement

• There are two physical mechanisms that keep track
  of body position.
• Vestibular sense The sense of body orientation
  with respect to gravity
• The receptors for this information are tiny hairs
  in the semicircular canal of the inner ear.

Vestibular System
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Position and Movement

• The kinesthetic sense keeps track of body parts,
  relative to each other.
• Kinesthesis provides constant sensory feedback
  about what the muscles in your body are doing.
• Receptors for kinesthesis reside in joints,
  muscles and tendons. These receptors are usually
  automatic, unless the person is learning a new
  skill.

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Smell

• The sense of smell is olfaction.
• Odors first interact with receptor proteins
  associated with hairs in the nose.
• The hairs convey information to the brains
  olfactory bulbs, located on the underside of the
  brain.
• In humans, olfaction has a close connection with
  memory.
• Certain smells, such as a favorite perfume, can
  evoke emotion-laden memories.

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Taste

• The sense of taste is gustation.
• Human taste has four main qualities sweet, sour,
  bitter and salty.
• Specialized nerves carry nothing but the taste
  messages to the brain. There taste is realized on
  a specialized region of the parietal lobes
  somatosensory cortex.

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Taste

• Taste receptors can be easily damaged by alcohol,
  smoke, acids or hot foods.
• Fortunately, gustatory receptors are frequently
  replaced.

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The Skin Senses

• Skin senses are also connected to the
  somatosensory cortex.
• The skins sensitivity to stimulation varies
  tremendously over the body, depending on the
  number of receptors in each area.

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Gate-Control Theory

• Gate-control theory An explanation for pain
  control that proposes we have a neural gate
  that can, under some circumstances, block
  incoming pain.
• Pain is sensed by two different sensory pathways,
  one moving very fast, one moving slower.
• The level of pain one feels results from the
  combination of information from both pathways.

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Gate-Control Theory

• Ultimately, pain signals are routed to the
  anterior cingulate cortex located along the
  fissure separating the frontal lobes.
• Pain medication works by blocking the faster of
  the two neural pathways.

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Perception

• Chapter 4

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Perception

• Perception A mental process that elaborates and
  assigns meaning to the incoming sensory patterns.
• Perception brings meaning to sensation. It
  produces an interpretation of the world, but it
  isnt a perfect representation.

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Feature Detectors

• Our brains have specialized cells whose job it is
  to identify specific features of a stimuli.
• We do not know how the brain combines these
  features to make a single percept. This problem
  is known as the binding problem.

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Bottom-Up and Top-Down

• Bottom-Up processing Analysis that emphasizes
  the characteristics of the stimuli rather than
  our concepts and expectations.
• Top-Down perception Analysis that emphasizes the
  perceivers expectations, concept memories and
  other cognitive factors, rather than individual
  characteristics.

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Describe This Picture
The Forest Has Eyes by Bev Doolittle

• Bottom-Up Lines, angles and colorsa guy riding
  a horse through the forest
• Top-Down We consider the title and direct our
  attention to aspects that will give meaning to it.

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Perceptual Consistency

• The ability to recognize the same object as
  remaining constant under changing conditions is
  called perceptual consistency.
• There are three examples of perceptual
  consistency including size (different distances),
  color (different lighting) and shape (different
  angles).

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Illusions

• Sometimes your mind will play a trick on you and
  interprets a stimulus incorrectly.
• When your mind interprets an image that is
  demonstrably incorrect, it is called an illusion.
  
• Lets look at an illusion!

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The Hermann Grid

• Stare at the center of grid. Note how dark fuzzy
  spots appear at the intersections of the white
  bars.
• Now focus on the intersections, there are no
  spots.
• Why does this illusion exist?

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The Answer

• The reason for this illusion lies in the way the
  receptor cells in your visual pathway interact
  with each other.
• The firing of certain cells that are sensitive to
  light-dark boundaries inhibits other cells that
  would detect the white lines. This blocking
  process makes you sense darker regions.

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Other Illusions at the Perceptual Level
Ebbinghaus Illusion
Poggendorf Illusion
Zollner Illusion
Muller-Lyer Illusion
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How Many Faces Do You See?
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More Illusions at the Perceptual Level
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Muller-Lyer Illusion

• One theory for why this illusion exists is that
  we unconsciously interpret the lines as 3D
  images. We see the ends as angles that point
  toward us or away from us. Therefore, we judge
  the outside corner to be closer and shorter.
• But what if you lived in a culture that had no
  square-cornered buildings?

Muller-Lyer Illusion
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The Zulus

• This questions was addressed in the 1970s when
  scientists took this image to South Africa and
  the Zulu people who live in a rounded culture.
• Almost exclusively, the Zulu perceived the lines
  as being the same size.
• What does this lead us to conclude about
  perception? (Hint learned or inherited?)

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More Illusions

• http//www.lifesci.sussex.ac.uk/home/George_Mather
  /Motion/index.html

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The Gestalt Theory

• Gestalt Psychologists argue that the brain forms
  a perceptual whole that is more than the mere sum
  of its sensory parts.

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Pre-wired

• Humans see a square as a single figure rather
  than four lines.
• Psychologists argue that examples like this show
  that humans organize sensory information into
  meaningful patters. The most basic of these
  patterns are pre-wired into our brains at birth.

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Figure and Ground

• Gestalt Psychology divides perceptual experience
  into figure and ground.
• Figure The part of a pattern that commands
  attentionstands out.
• Ground The part of the pattern that does not
  command attentionbackground.

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Closure Filling in the Blanks

• Our minds to a funny thing. They provide closure.
  That is, they make us see incomplete images as
  wholes by supplying the missing segments or
  filling in gaps.
• Generally, humans have a natural tendency to
  perceive stimuli as compete and balanced even
  when the pieces are missing.

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What shapes do you see in each image?
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Law of Perceptual Grouping

• Law of Similarity The Gestalt principle that we
  tend to group similar objects together in our
  perceptions.
• Do you see x o x o x
• rows or x o x o x
• columns? x o x o x
• x o x o x
• x o x o x

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Law of Perceptual Grouping

• Law of Proximity The Gestalt principle that we
  tend to group objects together when they are near
  each other.
• Do you see 5 Xs and 5 Os, or 5 pairs of Xs and
  Os?
• XO XO XO XO XO

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Law of Perceptual Grouping

• Law of Continuity The Gestalt principle that we
  prefer percepts of connected and continuous
  figures to disconnected and disjointed ones.
• Are these two continuous lines, or do they have
  breaks?

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Law of Perceptual Grouping

• Law of Common Fate The Gestalt principle that we
  tend to group similar objects together that share
  a common motion or destination.
• Think a school of fish, a flock of seagulls, a
  murder of crows

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Laws of Perceptual Grouping

• Law of Pragnanz The Gestalt principle which
  states that the simplest organization, requiring
  the least cognitive effort, will emerge as the
  figure.

What is wrong with this image?
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Context and Expectations

• Humans often use context to help interpret out
  sensations. Once you identify a context, you form
  expectations about what you are likely to
  experience.
• Context is an enormously useful cue to identify
  ambiguous stimuli.

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Perceptual Set

• Perceptual set is a readiness to detect a
  particular stimulus in a given situationthink of
  when you are afraid and staying home alone and
  you notice every noise and think it is a threat.
• Here is another example. What is the last word in
  each line?
• FOX OWL SNAKE TURKEY SWAN D?CK
• BOB RAY DAVE BILL TOM D?CK

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Which monster is bigger?
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Cultural Influences on Perception

• Look at the Ponzo Illusion below.
• Which line appears longer?

A
B
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Cultural Influences on Perception

• To most of us, like A looks longer.
  Psychologist says this may be a result of the
  culture we have grown up in which includes
  structures with long parallel lines that seem to
  converge in the distance.
• People who live in cultures without these such
  lines, like those in Guam see them as the same
  length. There are no long, straight railroad
  tracks or roads in Guam.

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Cultural Influences on Perception

• Research has supported the conclusion that people
  who live in cultures without long, parallel
  figures are less likely to report the top line
  being the longer figure.
• These results strongly support the argument that
  a persons experiences affect their perceptions.

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A Music Experiment

• Now we will do an experiment based on music and
  perception.
• For this experiment, all you have to do is sit
  back and enjoy the music.

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Good Music-Cultural Context

• Subway Concert
• Concert Show
• A description of the study

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A Matter of Perception

• In January of 2007, the Washington Post did a
  social experiment about perception. They had
  Joshua Bell, one of the world top violinists,
  play during the morning commute at a Washington
  subway station. Though over 1,000 people walked
  by, few stayed to listen. The week prior Bell
  filled a concert hall in Boston with tickets
  selling for over 100.

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The End

• If you assume your senses give you an accurate
  and undistorted picture of the world, you are
  probably wrong. If you dont believe me, try
  this.
• Silently read the backwards statement below. Flip
  if over in your mind. What does it say?
• .rat eht saw tac ehT

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Answer

• How many people saw this
• The cat saw the rat.
• Look at it again
• .rat eht saw tac ehT
• How many people saw this
• The cat was the rat.
• Answer
• The cat was the tar.